2008 YAMAHA YZ450F Owners Manual

5-40
REAR SHOCK ABSORBER
3. Install:
• Lower bearing "1"
Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
INSTALLING THE SPRING (REAR
SHOCK ABSORBER)
1. Install:
• Spring "1"
• Upper spring guide "2"
• Lower spring guide "3"
2. Install:
• Spring seat "1"
Install the spring seat with the projec-
tion "a" brought into contact with the
spring end, as shown.
3. Tighten:
•Adjuster "1"
4. Adjust:
• Spring length (installed)
Refer to "ADJUSTING THE
REAR SHOCK ABSORBER
SPRING PRELOAD" section in
the CHAPTER 3.
5. Tighten:
• Locknut "1"
INSTALLING THE REAR SHOCK
ABSORBER
1. Install:
• Dust seal "1"
• O-ring "2"
• Collar "3"
• Apply the molybdenum disulfide
grease on the dust seal lips and col-
lars.
• Apply the lithium soap base grease
on the O-rings.
2. Install:
• Bushing "1"
• Collar "2"
• Dust seal "3"
• Apply the molybdenum disulfide
grease on the bearing and dust seal
lips.
• Install the dust seals with their lips
facing outward.
3. Install:
• Rear shock absorber
4. Install:
• Bolt (rear shock absorber-frame)
"1"
• Washer "2"
• Nut (rear shock absorber-frame)
"3"
Apply the molybdenum disulfide
grease on the bolt.
5. Install:
• Bolt (rear shock absorber-relay
arm) "1"
• Nut (rear shock absorber-relay
arm) "2"
Apply the molybdenum disulfide
grease on the bolt.
6. Install:
• Rear frame "1"
• Bolt [rear frame (upper)] "2" Installed depth of the
bearing "a":
4 mm (0.16 in)
Nut (rear shock absorb-
er-frame):
56 Nm (5.6 m•kg, 40
ft•lb)
Nut (rear shock absorb-
er-relay arm):
53 Nm (5.3 m•kg, 38
ft•lb)
Bolt [rear frame (upper)]:
38 Nm (3.8 m•kg, 27
ft•lb)

5-41
REAR SHOCK ABSORBER
• Bolt [rear frame (lower)] "3"
7. Tighten:
• Bolt (air filter joint) "1"Bolt [rear frame (lower)]:
32 Nm (3.2 m•kg, 23
ft•lb)
Bolt (air filter joint):
3 Nm (0.3 m•kg, 2.2
ft•lb)

6-1
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
ELECTRICAL
ELECTRICAL
COMPONENTS AND
WIRING DIAGRAM
ELECTRICAL COMPONENTS
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch4. CDI magneto
5. Ignition coil
6. Spark plug7. CDI unit
WIRING DIAGRAM
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch
4. CDI magneto
5. Ignition coil
6. Spark plug
7. CDI unitCOLOR CODE
BBlack
Br Brown
GGreen
LBlue
O Orange
PPink
RRed
Sb Sky blue
WWhiteY Yellow
B/L Black/Blue
B/W Black/White
B/Y Black/Yellow
G/B Green/Black
L/W Blue/White
R/W Red/White
B/WB/W
B/L
B/Y
SbSb
G/B
LYLY
P
B
B
B
B
G
O
WR
P
GW
R P
B Br W
W
B/Y GBr
G RR
OB Sb Sb Y
Y
WY
W
GG
B
PP
Br BrR R
OL
B SbY LL
B/L B/W B/WG/B
B B
B/L L Sb
B/L
G/B
G/BB/Y
B/Y
B/W
O B/W
BrBrP
6

6-2
IGNITION SYSTEM
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to ignition system failure
and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
• Remove the following parts before inspection.
1. Seat
2. Fuel tank
• Use the following special tools in this inspection.
Spark gap test Spark→*Clean or replace spark plug.
No spark
↓
Check entire ignition system for connection.
(couplers, leads and ignition coil)No good→Repair or replace.
OK
↓
Check engine stop switch. No good→Replace.
OK
↓
Check ignition coil. (primary coil and secondary
coil)No good→Replace.
OK
↓
Check CDI magneto. (pickup coil and charging
coil)No good→Replace.
OK
↓
Check neutral switch. No good→Repair or replace.
OK
↓
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-3112-C/90890-03112

6-3
IGNITION SYSTEM
SPARK GAP TEST
1. Disconnect the ignition coil from
spark plug.
2. Remove the ignition coil cap.
3. Connect the dynamic spark tester
"1" (ignition checker "2") as
shown.
• Ignition coil "3"
• Spark plug "4"
A. For USA and CDN
B. Except for USA and CDN
4. Kick the kickstarter crank.
5. Check the ignition spark gap.
6. Start engine, and increase spark
gap until misfire occurs. (for USA
and CDN only)
CHECKING THE COUPLERS,
LEADS AND IGNITION COIL
CONNECTION
1. Check:
• Couplers and leads connection
Rust/dust/looseness/short-circuit
→Repair or replace.
• Ignition coil and spark plug as
they are fitted
Push in the ignition coil until it
closely contacts the spark plug
hole in the cylinder head cover.
CHECKING THE ENGINE STOP
SWITCH
1. Inspect:
• Engine stop switch conductionNot conductive while it is pushed
→
Replace.
Conductive while it is freed
→Re-
place.
Set the tester selection position to
"
Ω × 1".
CHECKING THE IGNITION COIL
1. Remove the ignition coil cap.
2. Inspect:
• Primary coil resistance
Out of specification
→Replace.
3. Inspect:
• Secondary coil resistance
Out of specification
→Replace.4. Inspect:
• Sealed portion of ignition coil "a"
• Spark plug terminal pin "b"
• Threaded portion of spark plug "c"
Wear
→Replace.
CHECKING THE CDI MAGNETO
1. Inspect:
• Pickup coil resistance
Out of specification
→Replace.
2. Inspect:
• Charging coil 1 resistance
Out of specification
→Replace. Minimum spark gap:
6.0 mm (0.24 in)
Tester (+) lead
→Black/White
lead "1"
Tester (-) lead
→Black lead "2"
Result
Conductive (while the
engine stop switch is
pushed)
Tester (+) lead
→Orange lead "1"
Tester (-) lead
→Black lead "2"
Primary
coil resis-
tanceTester se-
lector posi-
tion
0.08–0.10
Ω at 20 °C
(68 °F) Ω × 1
Tester (+) lead
→Orange lead "1"
Tester (-) lead
→Spark plug termi-
nal "2"
Secondary
coil resis-
tanceTester se-
lector posi-
tion
4.6–6.8
k
Ωat 20 °C
(68 °F) kΩ × 1
Tester (+) lead→Red lead "1"
Tester (-) lead
→White lead "2"
Pickup coil
resistanceTester se-
lector posi-
tion
248-372
Ω
at 20 °C (68
°F)Ω ×100
Tester (+) lead
→Brown lead "1"
Tester (-) lead
→Green lead "2"
Charging
coil 1 resis-
tanceTester se-
lector posi-
tion
720-1,080
Ω at 20 °C
(68 °F)Ω ×100

6-4
IGNITION SYSTEM
3. Inspect:
• Charging coil 2 resistance
Out of specification
→Replace.
CHECKING THE NEUTRAL
SWITCH
1. Inspect:
• Neutral switch conduction
Not conductive while it is in neutral
→
Replace.
Conductive while it is engaged
→Re-
place.
Set the tester selection position to
"
Ω × 1".
CHECKING THE CDI UNIT
Check all electrical components. If no
fault is found, replace the CDI unit.
Then check the electrical compo-
nents again.Tester (+) lead
→Pink lead "1"
Tester (-) lead
→Black lead "2"
Charging
coil 2 resis-
tanceTester se-
lector posi-
tion
44-66
Ω at
20 °C (68
°F)
Ω ×10
Tester (+) lead
→Sky blue lead
"1"
Tester (-) lead
→Ground "2"
Result
Conductive (while gear
is in neutral)

6-5
THROTTLE POSITION SENSOR SYSTEM
THROTTLE POSITION SENSOR SYSTEM
INSPECTION STEPS
If the throttle position sensor will not operate, use the following inspection steps.
*marked: Refer to "IGNITION SYSTEM" section.
Use the following special tools in this inspection.
Check entire ignition system for connection. No good→Repair or replace.
OK
↓
Check throttle position sensor. (Throttle position
sensor coil)No good→Replace.
OK
↓
*Check CDI magneto. (Charging coil) No good→Replace.
OK
↓
Check CDI unit. (Throttle position sensor input
voltage)No good→Replace.
Pocket tester:
YU-3112-C/90890-03112

6-6
THROTTLE POSITION SENSOR SYSTEM
HANDLING NOTE
Do not loosen the screw (throttle
position sensor) "1" except when
changing the throttle position sen-
sor due to failure because it will
cause a drop in engine perfor-
mance.
CHECKING THE COUPLERS AND
LEADS CONNECTION
1. Check:
• Couplers and leads connection
Rust/dust/looseness/short-circuit
→Repair or replace.
CHECKING THE THROTTLE
POSITION SENSOR COIL
1. Inspect:
• Throttle position sensor coil resis-
tance
Out of specification
→Replace.
2. Loosen:
• Throttle stop screw "1"
Turn out the throttle stop screw until
the throttle shaft is in the full close po-
sition.
3. Inspect:
• Throttle position sensor coil vari-
able resistance
Check that the resistance in in-
creased as the throttle grip is
moved from the full close position
to the full open position.
Out of specification
→Replace.
CHANGING AND ADJUSTING THE
THROTTLE POSITION SENSOR
1. Remove:
• Throttle position sensor coupler
• Carburetor
2. Remove:
• Screw (throttle position sensor)
"1"
• Throttle position sensor "2"
Loosen the screw (throttle position
sensor) using the T25 bit.
3. Replace:
• Throttle position sensor
4. Install:
• Throttle position sensor "1"
• Screw (throttle position sensor)
"2"
• Align the slot "a" in the throttle posi-
tion sensor with the projection "b"
on the carburetor.• Temporarily tighten the screw
(throttle position sensor).
5. Install:
•Carburetor
• Throttle position sensor coupler
6. Adjust:
• Engine idling speed
Refer to "ADJUSTING THE EN-
GINE IDLING SPEED" section in
the CHAPTER 3.
7. Insert the thin electric conductors
"2" (lead) into the throttle position
sensor coupler "1", as shown, and
connect the tester to them.
• Do not insert the electric conduc-
tors more than required because
it may reduce the waterproof
function of the coupler.
ŒMake sure that a short-circuit
does not develop between the
terminals because it may cause
damage to electrical compo-
nents.
8. Start the engine.
9. Adjust:
• Throttle position sensor output
voltage
Adjustment steps:
a. Adjust the installation angle of the
throttle position sensor "1" to ob-
tain the specified output voltage.
Measure the output voltage accurate-
ly with a digital electronic voltmeter
that gives an easy reading of a small
voltage.
Tester (+) lead→Blue lead "1"
Tester (-) lead
→Black lead "2"
Throttle po-
sition sen-
sor coil
resistanceTester se-
lector posi-
tion
4–6 k
Ω at
20°C (68 °F) kΩ×1
Tester (+) lead→Yellow lead "1"
Tester (-) lead
→Black lead "2"
Throttle position
sensor coil vari-
able resistanceTester
selec-
tor po-
sition
Full
closedFull
opened
k
Ω×1 Zero –2
kΩat
20°C
(68 °F)4–6
kΩat
20 °C
(68 °F)
Tester (+) lead→Yellow lead "3"
Tester (-) lead
→Black lead "4"